Influence Of Solid Retention Time Research Articles

Influence of Solid Retention Time on Membrane Fouling and Biogas Recovery in Anerobic Membrane Bioreactor Treating Sugarcane Industry Wastewater in Sahelian Climate.

Sugarcane industries produce wastewater loaded with various pollutants. For reuse of treated wastewater and valorization of biogas in a Sahelian climatic context, the performance of an anaerobic membrane bioreactor was studied for two solid retention times (40 days and infinity). The pilot was fed with real wastewater from a sugarcane operation with an organic load ranging from 15 to 22 gCOD/L/d for 353 days. The temperature in the reactor was maintained at 35 °C. Acclimatization was the first stage during which suspended solids (SS) and volatile suspended solids (VSS) evolved from 9 to 13 g/L and from 5 to 10 g/L respectively, with a VSS/SS ratio of about 80%. While operating the pilot at a solid retention time (SRT) of 40 days, the chemical oxygen demand (COD) removal efficiency reached 85%, and the (VSS)/(TSS) ratio was 94% in the reactor. At infinity solid retention time, these values were 96% and 80%, respectively. The 40-day solid retention time resulted in a change in transmembrane pressure (TMP) from 0.0812 to 2.18 bar, with a maximum methane production of 0.21 L/gCOD removed. These values are lower than those observed at an infinite solid retention time, at which the maximum methane production of 0.29 L/gCOD was achieved, with a corresponding transmembrane pressure variation of up to 3.1 bar. At a shorter solid retention time, the fouling seemed to decrease with biogas production. However, we note interesting retention rates of over 95% for turbidity.

Influence of the solids retention time on the formation of the microalgal-bacterial aggregates produced with municipal wastewater

The easy separation of the microalgal-bacterial biomass is crucial during wastewater treatment. Aggregates present excellent settling properties to enhance biomass separation. This paper evaluated the influence of solids retention time (SRT) on the formation of microalgal-bacterial aggregates during the treatment of municipal wastewater in continuous high-rate algal ponds (HRAP). Three SRT (6, 12, and 18 days) were studied in two 80 L HRAP operated at a fixed hydraulic retention time of 6 days. The aggregates formation was characterized by evaluating size distribution, settling properties, and biochemical composition, while the performance of the HRAP was evaluated considering the organic matter, suspended solids, nitrogen, and phosphorous removal. It was evidenced that the increment in the SRT in continuous HRAP favored the formation of the granular structures and settling properties impacting, therefore, in the effective solids' separation. No significant differences were found for COD removal, and bromatological characteristics for the three SRT evaluated. However, the increment on the SRT significantly affected the removal of N-NH4+, P-PO43− and suspended solids in the effluent, obtaining the best performances for an SRT of 12 days. It was found that the SRT imposes a community selectivity, allowing the formation of the aggregates. The increase in solids retention time induced the change from floccular aggregates to granules with an increment in the settling velocity (up to 7.4 m h−1). Microbiological characterization showed that aggregation depends on filamentous algae, cyanobacteria, and diatoms developed when the HRAP is operated under an SRT higher than 12 day

Influence of Solids Retention Time on Membrane Fouling in an Anmbr Treating Lipid-Rich Dairy Wastewater

Influence of Solids Retention Time on Membrane Fouling in an Anmbr Treating Lipid-Rich Dairy Wastewater

Genome-centric microbiome analysis reveals solid retention time (SRT)-shaped species interactions and niche differentiation in food waste and sludge co-digesters

Co-digestion of food waste with sewage sludge is widely applied for waste stabilization and energy recovery around the world. However, the effect of solid retention time (SRT) on the microbial population dynamics, metabolism and interspecies interaction have not been fully elucidated. Here, the influence of SRTs (5-25 days) on the performance of the co-digestion system was investigated and state-of-the-art genome-centric metagenomic analysis was employed to uncover the dynamics and metabolic network of the key players underlying the well-functioned and poorly-functioned co-digestion microbial communities. The results of the microbial analyses indicated that SRT largely shaped microbial community structure by enriching the syntrophic specialist Syntrophomonas and CO2/H2 ( formate)-using methanogen Methanocorpusculum in the well-functioned co-digester operated at SRT of 25 days, while selecting acid-tolerant populations Lactobacillus at SRT of 5 days. The metagenome assembled genomes (MAGs) of key players, such as Syntrophomonadaceae, Methanocorpusculum, and Mesotoga, were retrieved, additionally, the syntrophic acetate oxidation plus hydrogenotrophic methanogenesis (SAO-HM) were proposed as the dominant pathway for methane production. The metabolic interaction in the co-digestion microbial consortia was profiled by assigning MAGs into functional guilds. Functional redundancy was found in the bacterial groups in hydrolysis step, and the members in these groups reduced the direct competition by niche differentiation.

Reducing bacterial aerosol emissions from membrane bioreactors: The impact of SRT and the addition of PAC and calcium

Bacterial aerosols resulting from membrane bioreactor (MBR) processes, which require excessive aeration in a confined space, are important to investigate because of their possible adverse effects on human health. This study investigated the influence of solid retention time (SRT) on bacterial aerosols from MBRs. Moreover, powdered activated carbon (PAC) and calcium were used to attenuate bacterial aerosol emissions from MBRs. The particulate matter (PM) emitted from the MBRs was reduced by 30.5 and 25.2% at SRTs of 20 and 80 d, respectively, compared to the level emitted at an SRT of 10 d. Total cell counts were similarly reduced at SRTs of 20 and 80 d. Longer SRTs also led to greater reductions in the particle size distribution of the sludge within 10 μm. Several factors in the MBR influenced the behavior of the bacterial aerosol emissions from the MBRs. This study showed that changes in viscosity and particle size induced by the SRT influenced the bacterial aerosol emissions in MBRs. Therefore, SRT was identified as an important design parameter affecting bacterial aerosol emissions in MBR processes. The amounts of particulate matter and bacterial aerosols were reduced in MBRs using PAC and calcium, both of which exerted an immediate effect on the bacterial aerosol emissions in MBRs by increasing the aerosol-particle size.

The influence of solid retention time on IFAS-MBR systems: analysis of system behavior

ABSTRACTA University of Cape Town Integrated Fixed-Film Activated Sludge Membrane Bioreactor (UCT-IFAS-MBR) pilot plant was operated at different values of the sludge retention time (SRT). Three SRTs were investigated at different durations: indefinitely, 30 and 15 days. The organic carbon, nitrogen and phosphorus removal, kinetic/stoichiometric parameters, membrane fouling tendency and sludge filtration properties were assessed. The findings showed that by decreasing the SRT, the pilot plant could maintain excellent carbon removal efficiencies throughout the experiments. In contrast, the biological carbon removal showed a slight nitrification and was slightly affected by the decrease of the SRT, showing high performance (approximately 91%, on average). Thus, the biofilm might have helped sustain the nitrification throughout the experiments. The average phosphorus removal performance increased slightly with a decrease in SRT, achieving the maximum efficiency (61.5%) at a SRT of 15 days. After a 30-day SRT, an increase in resistance due to pore blocking and a general worsening of the membrane filtration properties occurred.

The influence of solid retention time on IFAS-MBR systems: Assessment of nitrous oxide emission

The aim of the present study was to investigate the nitrous oxide (N2O) emissions from a moving bed based Integrated Fixed Film Activated Sludge (IFAS) - membrane bioreactor (MBR) pilot plant, designed according to the University of Cape Town (UCT) layout. The experimental campaign had a duration of 110 days and was characterized by three different sludge retention time (SRT) values (∞, 30 d and 15 d). Results highlighted that N2O concentrations decreased when the biofilm concentrations increased within the aerobic reactor. Results have shown an increase of N2O with the decrease of SRT. Specifically, an increase of N2O-N emission factor occurred with the decrease of the SRT (0.13%, 0.21% and 0.76% of influent nitrogen for SRT = ∞, SRT = 30 d and SRT = 15 d, respectively). Moreover, the MBR tank resulted the key emission source (up to 70% of the total N2O emission during SRT = ∞ period) whereas the highest N2O production occurred in the anoxic reactor. Moreover, N2O concentrations measured in the permeate flow were not negligible, thus highlighting its potential detrimental contribution for the receiving water body. The role of each plant reactor as N2O-N producer/consumer varies with the SRT variation, indeed the aerobic reactor was a N2O consumer at SRT = ∞ and a producer at SRT = 30 d.

Influence of solids retention time on membrane fouling: characterization of extracellular polymeric substances and soluble microbial products

The objective of this study was to investigate the influence of solids retention time (SRT) on membrane fouling and the characteristics of biomacromolecules. Four identical laboratory-scale membrane bioreactors (MBRs) were operated with SRTs for 10, 20, 40 and 80 days. The results indicated that membrane fouling occurred faster and more readily under short SRTs. Fouling resistance was the primary source of filtration resistance. The modified fouling index (MFI) results suggested that the more ready fouling at short SRTs could be attributed to higher concentrations of soluble microbial products (SMP). Fourier transform infrared (FTIR) spectra indicated that the SRT had a weak influence on the functional groups of the total extracellular polymeric substances (TEPS) and SMP. However, the MBR under a short SRT had more low-molecular-weight (MW) compounds (<1 kDa) and fewer high-MW compounds (>100 kDa). Aromatic protein and tryptophan protein-like substances were the dominant groups in the TEPS and SMP, respectively.

Improved production of short-chain fatty acids from waste activated sludge driven by carbohydrate addition in continuous-flow reactors: Influence of SRT and temperature

During anaerobic fermentation of waste activated sludge (WAS), the production of short-chain fatty acids (SCFAs), especially propionic acid which is considered as the most preferred carbon source for enhanced biological phosphorus removal, can be improved by controlling the suitable mass ratio of carbon to nitrogen (C/N) and pH in batch mode. In this study the influences of solids retention time (SRT) and temperature on WAS hydrolysis and acidification in the continuous-flow systems in which the C/N ratio of WAS was modified by carbohydrate addition were investigated. Experimental results showed that the increase of SRT and temperature in a pertinent range benefited the hydrolysis of fermentation substrates and the accumulation of SCFAs, and SRT 8d and temperature 37°C were the most preferred conditions for the production of SCFAs, especially propionic acid. As there were more consumption of protein and carbohydrate and less production of methane at SRT 8d and temperature 37°C, more SCFAs were accumulated. Also, both the activities of key hydrolases and acid-forming enzymes and the ratio of acidogenic bacteria to methanogens showed good agreements with SCFAs production.

The influence of solids retention time on activated sludge bioflocculation and membrane fouling in a membrane bioreactor (MBR)

Membrane fouling remains a significant drawback for membrane bioreactors (MBRs). The solids retention time (SRT) has been widely acknowledged to be an important factor influencing membrane fouling. In general, lower membrane fouling rates are observed at elevated SRTs, however, the direct mechanisms through which a high SRT alleviates fouling are unclear. Since it has also been reported that activated sludge bioflocculation is an important factor in membrane fouling, this paper studies the impact of SRT on bioflocculation with respect to membrane fouling. A pilot-scale MBR was operated for more than two years at three different SRTs during which bioflocculation was closely monitored by means of an automated image analysis procedure while the fouling rate was recorded on-line for different fluxes and different filtration/relaxation cycles. In addition, the Delft filtration characterization method (DFCm) was employed to assess the activated sludge fouling propensity. Based on these data, it is shown that stable operation of a membrane bioreactor requires a good activated sludge condition and that bioflocculation is a crucial factor within that context. In the tested SRT range (10–30–50 days), a higher SRT contributes to better activated sludge bioflocculation and as a consequence, to lower fouling rates.

Influence of solids retention time on continuous H2 production using membrane bioreactor

H2 production Solids retention time Specific loading rate Membrane bioreactor Butyric acid Extracellular polymeric substances abstract The influence of solids retention time (SRT) on continuous H2 production in a submerged membrane bioreactor (MBR) was investigated using mixed mesophilic microflora. The bioreactor was continuously operated at the four SRTs of 2, 4, 12.5 and 90 d on a glucose medium under the hydraulic retention time (HRT) of 9 h and the mesophilic condition of 35 � C � 0.5. Stable biogas production with H2 content of 50.8%-60% was achieved at SRTs ranging from 2 to 12.5 d. No methane gas was observed in monitoring the experimental conditions. The H2 production increased from 17.62 to 26.1 l-H2/d when the SRT increased from 2 to 12.5 d, but decreased to 9.1 l-H2/d at the 90 d SRT. The best H2 yield, 1.19 mol-H2/ mol-glucose, was observed at the SRT of 2 d and the highest H2 production rate, 5.8 l-H2/l/ d, was obtained at the SRT of 12.5 d. Stable H2 production was achieved by maintaining the SRT in the range of 2 - 12.5 d, regardless of the fermentative pathway related to higher lactate production. The decrease in H2 yield was observed at long SRTs due to the low volatile suspended solids/total suspended solids (VSS/TSS) as well as the high extracel- lular polymeric substances (EPS) concentrations. These results suggest that the SRT is the key factor enabling sustainable H2 fermentation in MBR, and that an SLR value of around 1.6 kg-DOC/kg-VSS/d might be the specific condition for achieving optimum H2 production.

Influence of solid retention time on sludge characteristics and effluent quality in immersed membrane bioreactor

Here the effect of solid retention time (SRT) on the concentration of the mixed liquor suspend solid (MLSS), the sludge characteristics, the content of extra-cellular polymeric substances (EPS), the viscosity of mixed liquor and effluent quality in the immersed membrane bioreactor (IMBR) was investigated. The results indicate that the increase of the EPS content is the main reason for the increase of mixed liquor viscosity, the former is positively correlated with the latter (R 2 = 0.9751). The size distribution profile of particles in the mixed liquor presents double-peak shape at SRT more than 30 days. The filtration resistance of membrane in IMBR is mainly caused by the tiny particles and the viscosity of the mixed liquor. In this study, the extension of SRT can hardly affect the removal efficiency of Chemical Oxygen Demand (COD) and NH4 +-N, and when SRT is below 30 days, silt density index (SDI15) is less than 3, the effluent can be deeply treated by using reverse osmosis system (RO) or nano-filtration system (NF). The method of controlling SRT is put forward by analyzing the relationship between SRT and the minimum generation-time of dominant bacteria (at the maximum specific growth rate under the operation temperature).

Fermentation and elutriation of primary sludge: Effect of SRT on process performance

A primary sludge fermentation–elutriation pilot plant was operated using in-line and side-stream schemes. The influence of solids retention time, recirculation sludge flow-rate and solids concentration on the fermentation–elutriation process performance has been assessed in this paper. The use of high elutriation flows (12% of influent flow) improved the volatile fatty acids (VFA) concentration in the effluent stream. Suspended solids removal efficiency decreased in the primary settler when the solids retention time (SRT) was increased from 4 to 8 days. Disintegration step during hydrolysis process was pointed out as the main reason for that decrease. Maximum VFA productions were achieved at SRT between 6 and 8 days at the highest elutriation flow tested for both configurations. Propionic, butyric and valeric volatile fatty acids percentage increased when total solids sludge concentrations above 23,000 mg l −1 were used. Hydrogen accumulation, causing acetogenic bacteria inhibition, was indicated as the reason for C 3–C 5 fatty acids accumulation.

Carbamazepine as a possible anthropogenic marker in the aquatic environment: investigations on the behaviour of Carbamazepine in wastewater treatment and during groundwater infiltration

Sewage treatment plant (STP) effluents are significant sources of pharmaceutical residues in surface waters, where high concentrations of the antiepileptic drug Carbamazepine have been detected. The solids retention time (SRT) is the most important parameter for the design of STPs. It relates to the growth rate of microorganisms and to effluent concentrations. The influence of SRT on the removal of Carbamazepine was studied on lab-scale plants. The results from these tests were then validated on several full-scale plants. Due to the lack of suitable receiving waters and groundwater resources, one of these STPs has to infiltrate the treated wastewater into unsaturated soil. Here, groundwater samples at equal distances from the infiltration point were taken to estimate the behaviour of Carbamazepine during soil passage and within the groundwater. This antiepileptic drug seems to be very persistent in the environment, therefore qualifying as a suitable marker for anthropogenic influences in the aquatic environment.

Effect of solids retention time on floc structure

Correlative microscopy was applied to study the influence of solids retention time on activated sludge floc structure. Conventional optical microscopy revealed flocs at lower SRTs (4 and 9 days) to be irregular in shape while flocs at higher SRTs (16 and 20 days) had a more spherical and compact structure. Flocs were examined by environmental scanning electron microscopy (ESEM) and by transmission electron microscopy (TEM) coupled with energy-dispersive spectroscopy (EDS). Distinctive differences in floc structure and the arrangement of EPS were revealed. Flocs from higher SRTs were less hydrated and were found to possess a dense EPS layer that covers much of the surface. Extracellular osmiophilic granules present in these flocs indicate that the cells at the higher SRT may produce more lipid-like material. This EPS layer appears to decrease the floc surface roughness and protects the interior cells from disruption by changes in the external environment. Sludge flocs at higher SRTs were found to be physically more stable than those at lower SRTs.

The influence of cadmium on activated sludge activity

The influence of solid retention time, cadmium loading and the effect of the process of acclimation on the activity of activated sludge in the presence of the metal were studied. Activated sludge was cultivated in plug-flow and continuous completely mixed lab-scale bioreactors. Respirometric measurements were applied to evaluate the inhibition effects of cadmium on activated sludge. Monod's equation and the equation of non-competitive inhibition were applied to describe the toxicity and inhibition of cadmium. Maximum inhibition effect of cadmium was observed at different time periods of cadmium acting on both acclimated and non-acclimated sludges. The dependence of the attainment of maximum inhibition effect on the metal loading as well as solid retention time was observed. Therefore, maximum inhibition should be included in the assessment of metal toxicity.